The present invention relates to a method for determining the size of the stitch loops in high-speed sock-production machines and consequently the transverse stretchability of the socks, by means of a control unit.
It is known that the width of a sock is adjusted by varying the position in height of the stitch-formation triangles. It is thus possible to vary the depth of descent of the needle below the striking surface of the sinkers and consequently the length of thread taken up by each stitch loop.
The position in height of the triangles is adjusted by two step motors:
plain-stitch motor; PA1 purl-stitch motor. PA1 selecting two triangle height values; PA1 determining the specific lengths for these height values by measuring the drawing positions; and PA1 calculating each of the two values of the corresponding knitted product widths using the following equation: ##EQU3## wherein t is the specific length determined by the control unit, (t.sub.1,1.sub.1) and (t.sub.2, 1.sub.2) are the values of the two pairs formed by the specific length and corresponding width of the knitted product, and K is a conversion factor.
References made below to the step motor concern the plain-stitch motor. The position of the purl-stitch motor may be deduced from that of the plain-stitch motor and from coefficient P (percentage of the purl/plain stitches ratio) ##EQU1## where HR and HD are the position, in steps, of the purl-stitch motor and the position, in steps, of the plain-stitch motor respectively.
In the current state of the art, adjustment of the height is pre-set by the operator on the basis of his experience gained from numerous experiments.
The basic parameters in play for the height setting are the typology and type of the yarn, leaving the number of needles, speed of the yarn and percentage of the plain/purl-stitch ratio constant.